1. Field of the Invention
The present invention relates generally to fabrication of semiconductor integrated circuits, and more particularly to a structure and method for fabricating contact structures in integrated circuits.
2. Description of the Prior Art
Conductive interconnect layers typically have an enlarged area in the layer itself at a location where a contact is to be made from a later formed interconnect layer. Those skilled in the art commonly call the enlarged area the enclosure. Recognizing that errors in mask alignment can shift a contact from a desired location, the enclosure accounts for the errors in mask alignment by providing additional contact space. Thus, the enclosure ensures a contact will be made to an underlying interconnect layer.
A conflict arises, however, between the need for enclosures and the desire to reduce the chip sizes in integrated circuits. Those skilled in the art will recognize that there must be a minimum amount of space between adjacent conductive elements. Enclosures in an interconnect layer force the distance between adjacent conductive elements to increase in order to maintain the minimum distance between the adjacent conductive elements. Thus, the need for enclosures places restrictions on how small the size of an integrated circuit can be.
Errors in mask alignment can also cause problems during formation of the interconnect layers. Interconnect layers can be formed directly above an underlying conductive element, where ideally, the interconnect layer completely covers the underlying conductive element. Errors in mask alignment, however, allow for placement of the interconnect layer to shift from the desired location, causing a portion of the underlying conductive element to be exposed. During formation of the interconnect layer the underlying conductive element may be damaged as a result of the exposure. Damage to the conductive element can affect the reliability of the integrated circuit.
Therefore, it would be desirable to provide a method for forming contact structures which protects underlying conductive elements from damage during formation of interconnect layers. It is also desirable that such a method result in contact structures which are free from voids or other defects. Finally, it is desirable that such a method eliminate the need for enclosures in interconnect layers.